1. Field of the Invention
The present invention is directed to a detector for an X-ray computed tomography apparatus of the type having a number of detector elements of different widths separated from one another by septa, forming a detector line arranged in a direction of a rotational axis of the tomography apparatus, with a number of such detector lines being arranged next to each other, and wherein a predetermined number of channels are provided for acquiring signals generated by the detector elements, with one or more of the detector elements being selectively connectable to respective ones of the channels for acquiring the signals.
2. Description of the Prior Art
Detectors of the above general type are disclosed in German OS 195 02 574 and PCT Application WO 98/05980. They have a number of parallel detector lines that proceed in the direction of the axis of a subject to be transirradiated, for example a patient. Each detector line is composed of a number of detector elements that, for example, are manufactured of a scintillator ceramic.
For readout of the signals generated by the detector elements, usually four, currently at most eight, channels are available dependent on the computing power of the computer. Dependent on the demands regarding the desired image information, a number of detector elements lying next to one another in a detector line can be respectively connected to one channel. When, for example, two or more detector elements of a detector line are connected to one channel, information about a relatively large volume excerpt of the transirradiated subject is obtained. Such an information is especially well-suited for producing high-contrast images with which, for example, it is possible to differentiate soft parts in the brain.
When, in contrast, only one detector element from each line is respectively connected to each of the channels, the transirradiated volume is small. The information thus obtained is especially well-suited for the resolution of fine structures, for example in the inner ear region.
For gating the required, fan-shaped X-ray beam, a diaphragm precedes the known detector. The provision of such a diaphragm causes increased manufacturing outlay. Moreover, the detector has a number of detector elements with a number of septa separating them. The efficiency of such a detector is not especially high. The multitude of provided detector elements further increases the manufacturing outlay of the detector.
An object of the invention is provide a simply constructed, universal detector with enhanced efficiency for an X-ray computed tomography apparatus.
This object is achieved in accordance with the invention in a detector of the type initially described wherein the widths of the detector elements are selected such that a channel occupancy combination selected from the following group can be realized: [20xc3x97b1 or 20xc3x97b2 or 16xc3x97b4], [16xc3x97b1 or 16xc3x97b2 or 12xc3x97b4], [8xc3x97b1 or 8xc3x97b2 or 8xc3x97b4 or 8xc3x97b6], [4xc3x97b1 or 4xc3x97b2 or 4xc3x97b4 or 4xc3x97b8 or 4xc3x97b12], [8xc3x97b1 or 8xc3x97b2 or 8xc3x97b5], [4xc3x97b1 or 4xc3x97b2, 4xc3x97b4 or 4xc3x97b10], wherein the detector elements are designated b1 . . . b10.
In terms in the above, such as 20xc3x97b1 or 12xc3x97b4, for example, b1 designates a slice having a thickness equal 1 times the thickness of a detector element referenced b1, and b4 designates a slice having a thickness equal to 4 times the thickness of the detector element referenced b1. Slice combination 20xc3x97b1 can be scanned if 20 electronics channels are available, while 12 electronics channels are sufficient to stand the slice combination 12xc3x97b4.
A detector that enables the inventive channel combination can have a minimized number of septa with respect to the selected channel occupancy combination. The efficiency, particularly the quantum efficiency, of such a detector is enhanced. A diaphragm preceding the detector can be foregone. This, in particular, reduces the cost outlay for the manufacture of the X-ray computer tomograph.
Expediently, the septa are symmetrically arranged with reference to a symmetry plane of the detector line that proceeds perpendicular to the rotational axis. This further facilitates manufacture.
The detector elements have respective widths B1 . . . B10. A smallest, first width B1 can have a value selected from the following group: 0.375 mm, 0.5 mm, 0.625 mm, 0.75 mm, 1.0 mm. A tenth width B10 can amount to ten times, an eighth width B8 to eight times, a sixth width B6 to six times, a fifth width B5 to five times, a fourth width B4 to four times and a second width B2 to twice the first width B1. According to a further feature, the overall width of the detector line is 40 times, 48 times or 64 times the first width B1.